1. Field of the Invention
The invention relates to an ocean-wave spectrometer radar system for measuring the characteristics of gravity waves. More particularly, the invention relates to a coherent, stepped dual-frequency, microwave radar in which the stepped radar-return signals are multiplied and signal-processed to obtain gravity wave information.
2. Description of the Prior Art
Wave staffs, pressure sensors, current meters, cameras and laser profilometers have been used to measure the characteristics of ocean surface gravity waves having wavelengths of the order of meters to hundreds of meters and frequencies of the order of Hz or less. These methods all have deficiencies such as: disturbing the surface wave system; requiring deployment in awkward arrays to get directional information; operating in less than real time; and, in the case of the laser profilometer, requiring scanning through several directions.
Radar systems have also been used to measure ocean surface-wave properties and have the advantage that they are remote sensing instruments. Single-frequency microwave radars have been used to measure capillary wave amplitudes (i.e., centimeter wavelengths), as well as certain properties of longer waves (e.g., sea state of significant wave height). These single-frequency radars have two main disadvantages when used to measure gravity wave properties: they react to waves propagating in all directions; and they combine the effects of many wavelengths. A profile of the sea-surface reflectivity may be obtained with a high-resolution single-frequency radar. Such a radar, however, does not selectively respond to a single-wavelength gravity wave propagating in a preferred direction. High-frequency (HF) radars have been used to measure properties of gravity waves but are limited in their operation due to their large antenna size and the restriction that they cannot operate freely in the broadcast band.
A concurrently filed patent application, Navy patent application, Ser. No. 743,372, Dual Frequency, Remote, Ocean Wave Spectrometer by John W. Wright, William J. Plant and Dale L. Schuler, is an ocean-wave spectrometer radar system which utilizes radar reflections from capillary waves to measure the frequency and characteristics of gravity waves. This system overcomes the difficulties of the previously described prior-art systems but has the difficulty that it takes too long to measure the characteristics of a multiplicity of gravity waves. Sea-surface conditions may change in this period of time.